利用树的先序和后序遍历打印os中的目录树

【0】README

0.1）本代码均为原创，旨在将树的遍历应用一下下以加深印象而已；（回答了学习树的遍历到底有什么用的问题？）你对比下linux 中的文件树 和我的打印结果就明理了；

0.2）我们采用的是 儿子兄弟表示法 来 表示树的整体节点构造；

0.3）儿子兄弟表示法介绍

0.3.1）如下图所示： 向下的箭头（左指针）指向第一个儿子节点， 从左到右的箭头（右指针）指向下一个兄弟节点；（间接说明了树的节点有两个指针）

0.3.2）树节点定义代码如下：

struct Tree;typedef struct Tree *Tree;// we adopt child-sibling notationstruct Tree{    ElementType value;    Tree firstChild;    Tree nextSibling;};

0.4）哥子第一次 使用着 丑到逼爆 的 编辑器，也是醉了，主要是markdown 对于源代码文件显示不够清晰， oh m g；

【1】任务来了

我们想要列出目录中所有文件的名字， 我们的输出格式将是：深度为 depth 的文件的名字将被 depth 次跳格缩进后打印出来；

【2】给出先序遍历+后序遍历目录树的实现代码

2.1）先序遍历步骤：

step1）访问根节点；

step2）先序遍历以儿子为根的子树；

step3）先序遍历以兄弟为根的子树；

download source code：https://github.com/pacosonTang/dataStructure-algorithmAnalysis/blob/master/chapter4/p68_preorder_common_tree.c

source code at a glance：

#include <stdio.h>#include <malloc.h>#define ElementType char#define Error(str) printf("\n error: %s \n",str)   struct Tree;typedef struct Tree *Tree;Tree createTree();Tree makeEmpty(Tree t);Tree insert(ElementType e, Tree t);// we adopt child-sibling notationstruct Tree{ElementType value;Tree firstChild;Tree nextSibling;};// create a tree with root nodeTree createTree(){Tree t;t = (Tree)malloc(sizeof(struct Tree));    if(!t) {        Error("out of space, from func createTree");                return NULL;    }    t->firstChild = NULL;t->nextSibling = NULL;t->value = '/';return t;}// make the tree empty Tree makeEmpty(Tree t){if(t){makeEmpty(t->firstChild);makeEmpty(t->nextSibling);free(t);}return NULL;}//Tree insert(ElementType e, Tree parent){Tree child;Tree newSibling;if(!parent){Error("for parent tree node is empty , you cannot insert one into the parent node, from func insert");                return NULL;}newSibling = (Tree)malloc(sizeof(struct Tree));if(!newSibling) {        Error("out of space, from func insert");                return NULL;    }newSibling->value = e;newSibling->nextSibling = NULL;newSibling->firstChild = NULL;// building the node with value e overchild = parent->firstChild;if(!child) {parent->firstChild = newSibling;return parent;}while(child->nextSibling)child = child->nextSibling; // find the last child of parent nodechild->nextSibling = newSibling;return parent;}// find the tree root node with value equaling to eTree find(ElementType e, Tree root){Tree temp;if(root == NULL)return NULL;if(root->value == e)return root;temp = find(e, root->firstChild);if(temp) return temp;elsereturn find(e, root->nextSibling);}// analog print directories and files name in the tree, which involves preorder traversal.void printPreorder(int depth, Tree root){int i;if(root) {for(i = 0; i < depth; i++)printf("    ");printf("%c\n", root->value);printPreorder(depth + 1, root->firstChild);printPreorder(depth, root->nextSibling);} }int main(){Tree tree;tree = createTree();printf("\n test for insert 'A' 'B' into the parent '/' and 'C' 'D' into the parent 'A' \n");insert('A', tree);insert('B', find('/', tree));insert('C', find('A', tree));insert('D', find('A', tree));printPreorder(1, tree);printf("\n test for insert 'E' 'F' into the parent '/'  \n");insert('E', find('/', tree));insert('F', find('/', tree));printPreorder(1, tree);printf("\n test for insert 'G' 'H' into the parent 'E' and 'I' into the parent 'H' and even 'J' 'K' into the parent 'I' \n");insert('G', find('E', tree));insert('H', find('E', tree));insert('I', find('H', tree));insert('J', find('I', tree));insert('K', find('I', tree));printPreorder(1, tree);return 0;}

打印结果如下：

2.2）后序遍历步骤：（不同于二叉树的后序）

step1）后序遍历以儿子为根的子树；

step2）访问根节点；

step3）后序遍历以兄弟为根的子树；

download source code：https://github.com/pacosonTang/dataStructure-algorithmAnalysis/blob/master/chapter4/p69_postorder_commone_tree.c

source code at a glance:

#include <stdio.h>#include <malloc.h>#define ElementType char#define Error(str) printf("\n error: %s \n",str)   struct Tree;typedef struct Tree *Tree;Tree createTree();Tree makeEmpty(Tree t);Tree insert(ElementType e, Tree t);// we adopt child-sibling notationstruct Tree{ElementType value;Tree firstChild;Tree nextSibling;};// create a tree with root nodeTree createTree(){Tree t;t = (Tree)malloc(sizeof(struct Tree));    if(!t) {        Error("out of space, from func createTree");                return NULL;    }    t->firstChild = NULL;t->nextSibling = NULL;t->value = '/';return t;}// make the tree empty Tree makeEmpty(Tree t){if(t){makeEmpty(t->firstChild);makeEmpty(t->nextSibling);free(t);}return NULL;}//Tree insert(ElementType e, Tree parent){Tree child;Tree newSibling;if(!parent){Error("for parent tree node is empty , you cannot insert one into the parent node, from func insert");                return NULL;}newSibling = (Tree)malloc(sizeof(struct Tree));if(!newSibling) {        Error("out of space, from func insert");                return NULL;    }newSibling->value = e;newSibling->nextSibling = NULL;newSibling->firstChild = NULL;// building the node with value e overchild = parent->firstChild;if(!child) {parent->firstChild = newSibling;return parent;}while(child->nextSibling)child = child->nextSibling; // find the last child of parent nodechild->nextSibling = newSibling;return parent;}// find the tree root node with value equaling to eTree find(ElementType e, Tree root){Tree temp;if(root == NULL)return NULL;if(root->value == e)return root;temp = find(e, root->firstChild);if(temp) return temp;elsereturn find(e, root->nextSibling);}// analog print directories and files name in the tree, which involves postorder traversal. void printPostorder(int depth, Tree root){int i;if(root) {printPostorder(depth + 1, root->firstChild);for(i = 0; i < depth; i++)printf("    ");printf("%c\n", root->value);printPostorder(depth, root->nextSibling);} }int main(){Tree tree;tree = createTree();printf("\n ====== test for postordering the common tree presented by child_sibling structure  ====== \n");printf("\n test for insert 'A' 'B' into the parent '/' and 'C' 'D' into the parent 'A' \n");insert('A', tree);insert('B', find('/', tree));insert('C', find('A', tree));insert('D', find('A', tree));printPostorder(1, tree);printf("\n test for insert 'E' 'F' into the parent '/'  \n");insert('E', find('/', tree));insert('F', find('/', tree));printPostorder(1, tree);printf("\n test for insert 'G' 'H' into the parent 'E' and 'I' into the parent 'H' and even 'J' 'K' into the parent 'I' \n");insert('G', find('E', tree));insert('H', find('E', tree));insert('I', find('H', tree));insert('J', find('I', tree));insert('K', find('I', tree));printPostorder(1, tree);return 0;} 

打印结果如下：